The members of the chemotactic intercrine family, namely MCAF and IL 8 are transcriptionally and post transcriptionally regulated. Modulation of expression of these proteins can be stimulated by IL 1, TNF, PMA and PKF. Other immunomodulators such as dexamethasone can inhibit expression. Three dimensional analysis of these proteins using NMR and crystallography indicate that the amino terminal portion as well as the region around His 34 may be important for binding of IL 8 to its receptor. Competition studies with various ligands from the IL 8 family show that several ligands will bind to the IL 8 receptor though with different affinities. Present studies are underway to identify the binding regions and the nature of ligands responsible for the low affinity binding. Distinct species of IL 8 receptors have been identified on cross-linking gels. These receptors presumeably have a different primary amino acid sequence and different affinities for IL 7. The MCAF receptor is also capable of binding other ligands from the same class of intercrines with different affinities. A soluble receptor assay has been developed and employed to permit the biochemical study and purification of the MCAF receptor. The receptor is a glycoprotein with a molecular weight of approximately 38-40k. cDNA cloning of both the IL 8 and MCAF receptor is in progress.